I have a colt 6400c with the pinned open collapsable stock.  After the ban expires can you unpin it to make it collapsable?

Not sure about yours in particular, but a lot of the fake telestocks have a full length buffer and spring. Thus, they cannot be turned into the real thing.

I am not sure why this question keeps getting asked...

Look at your stock.  Does the buffer tube go all the way to the rear of the CAR stock as most all fake CAR stocks do?  If so, I hope you realize that you have a rifle length buffer tube.  

Now, I guess you "CAN" unpin the CAR stock and I am betting that you may need to cut the original stock from the buffer tube as some use an epoxy to help keep it where it belongs (I could be wrong... so let me know if you do it).

From there, you will need to cut down the full length buffer tube and weld a new end to the shortened buffer tube.  I also think you may need to drill new holes for the latch pin to engage to get your various positions.  When you are done you may also need to replace a few other parts depending on any dammage you do getting things apart, cut down, rewelded, and then reassembled...

Personally, I would buy a new one for about $60 but if you really want to try to do it it should be possible!

It has the short buffer tube with two pins that can be pressed or drilled out.

Quoted: It has the short buffer tube with two pins that can be pressed or drilled out.

If that is the case, it is possible but please let us know if you find that it really does have the full length buffer tube as every one I have looked at so far does!

Your right quarterbore, it is full length.  I thought it was short because of the short spring and buffer.  The last three inches of the buffer tube all the way to the end of the stock is solid with a small drain hole.  Is it difficult to replace one of these.  I have read the pdf for the magpul 93a, and the talk about shims starts to scare me.  Is the install easier with a stantard m4 stock.

Yes...  with a standard CAR stock you just unscrew the one you have and screw a new one on...  Just order a CAR wrench if you don't have one!

i almost bought one of those without looking very carefully.  i ASSUMED all it would take was a drill to make it legal.

i can't believe those asss would sell that configuration.

Pin this TTT, so many times asked yes. TACK IT!

Quoted: Yes...  with a standard CAR stock you just unscrew the one you have and screw a new one on...  Just order a CAR wrench if you don't have one!

This has been covered in depth before- but most probably didn't get to read it.
The bottom line is that Quarterbore knows his buffer-tube, buffer-spring, buffer-shit as good as any.
I'd go with him on this one